Liquid extraction processes and apparatus have long been known wherein stationary packings or trays are utilized to aid in the separation of the components of liquid phases being passed through the apparatus in either co-current flow or in countercurrent flow. Such processes and the apparatus for carrying out the same are, however, generally very inefficient. This is so since there simply is not enough energy, even in counterflowing liquid phase processes, to create efficient mass transfer. Consequently, as a general rule, extraction columns for carrying out such processes must be relatively large in terms of size in order to provide a height equivalent to a theoretical stage, known as HETS, which will result in reasonably efficient extraction columns of this type and HETS of 6 to 20 feet or more are quite common.
In order to overcome the disadvantages of such processes and extraction columns utilized to accomplish the same, early attempts were made to add energy to the extraction columns used by disposing in the columns a series of mixers on long vertical shafts both with and without interspersed zones of mesh material to permit coalescence of phases between mixers. While such columns are an improvement upon the earlier columns employing stationary packings or trays, they have drawbacks related to the development of very small droplets in the vicinity of the agitators or mixers. Another variation of this second generation of columns utilizes a series of mixer and settler chambers disposed side by side in a horizontal arrangement. However, even with the improvements attained by the second generation of columns, maximum efficiency still is not attained. However, the horizontal arrangement mentioned is expensive to construct and like other earlier models of extraction columns, requires a great deal of floor space.
Subsequent designs utilized continuous phase pulsation of liquids to be extracted through a stationary column. Columns so constructed, however, have achieved only limited commercial importance primarily due to the fact that it is difficult to keep agitation uniform throughout large columns and, furthermore, greater power requirements are necessary to move a large volume of liquids in such columns. Consequently, further developments resulted in columns which employ a series of perforated plates which can be reciprocated in a convenient manner. Even these columns, with uniform plate spacing, however, exhibit certain drawbacks with respect to HETS, other size and design factors and efficiency of operation with respect to volume of liquid phases being transported through such columns and liquid separation to be accomplished thereby. However, such perforated plate columns are generally more efficient than the precursor columns, such as those mentioned above, even though there still exists a need for further improvements in reciprocating plate columns to provide columns of this type which are smaller in size, as well as more efficient in overall operation. The present invention provides such an improved process and apparatus for accomplishing the same with respect to reciprocating plate extraction columns.